As the real estate market has declined, buyers at the Rushmore, at 80 Riverside Boulevard, have been trying to find ways out of their contracts. Now, buyers and the development’s sponsors, Extell Development and the Carlyle Group, have agreed that there was a mistake in the date given in the project’s offering plan. The plan said that buyers would be able to back out if the first closing did not occur before September 1, 2008, but the year given in the plan should have been 2009. The first closing took place in February of this year. Real estate attorney Richard Cohen has filed an application with the state attorney general’s office asking for deposit refunds for 23 Rushmore buyers. But Extell argues that the mistake in the offering plan was not significant. Cohen said many of the Rushmore buyers don’t actually want to leave the building, but they want to purchase their units at a lower price.